1. Field of the Invention
The present invention relates to display controllers architecture generally and especially to twisted nematic LCD controllers embedded in microcontrollers which interface to LCD displays but is not limited to this kind of displays and may address other types of display controllers.
2. The Prior Art
Integrated circuit driven display panels, especially passive Twisted Nematic Liquid Crystal Displays (TN LCD) have been well known for 30 years and can be found in many electronic devices, especially in battery powered devices such as watches, games, digital cameras and other devices.
When powered by batteries, the electronic device must reduce its consumption as much as possible to improve the battery lifetime. Therefore, reduced power modes of operation have been designed. As an example when only a single static image must be displayed, the powered circuitry can be limited to the display panel itself and the minimum logic circuitry to generate the displayed image rather than powering the entire microcontroller logic including the microprocessor.
When an application (watch, remote control, calculator, digital camera) is in standby/low power some images may still appear on the display to inform user about their mode of operation (standby, advertising). Such images often appear blinking, such as the well known colon in watch displays. More sophisticated displays may replace the blank period of the traditional blinking mode by presenting a different image, thus displaying more info, or impart visual dynamics to the displayed image.
To provide an attractive display when an electronic appliance is in use, images can be also changed from time to time. To do this, it is not possible to power only the display controller circuitry, but the application must also reload the new images. Therefore it is common practice to wake up the microprocessor and associated logic (PLL, memories, regulators, etc.) so that the software can reload an image into the holding/frame buffer of the display controller. When this task has been completed, the microprocessor and associated logic can be powered off to reduce power consumption.
Many LCD display controllers also include two buffers containing data to be displayed in order to correctly display an image when it is updated to minimize display flickering. A user buffer is provided to store updated image information. The display buffer is loaded from the user buffer (also known as a holding buffer) at a selected time slot location of the display frame. Even with such capabilities, from the application point of view there is only one frame that can be loaded in the display controller.